German-"Offenlegungsschrift" 36 28 706 A1 discloses a central locking system in which each actuator of the central locking system is connected via a bus system to a central control unit evaluating a plurality of state parameters of doors registered by signal sensors of a plurality of individual actuators. A plurality of state signals are delivered from the signal sensors which are then converted in the central control unit to control signals for controllers of the actuators in accordance with a stored program. These control signals in turn are fed via the bus system to the controllers.
German-"Offenlegungsschrift" DE 42 19 212 A1 describes furthermore a central locking system in which each actuator has a control unit of its own which is fed both with data signals from signal sensors of the actuator and with selected data signals from signal sensors of other remaining actuators in the central locking system. Each control unit retrieves the signal information of the individual signal sensors of its actuator and, on the basis of these data signals and in accordance with selected data signals of the other actuators, calculates control signals for controllers of the central locking system and a theft protection system which are associated with the respective actuator. For transmitting the selected data signals, there is provided a bus system transmitting signals issued by the actuators in a time-division multiplex transmission mode.
Furthermore, German-"Offenlegungsschrift" DE 195 18 306 A1 discloses an apparatus for controlling a plurality of mutually communicating actuators of a convenience control system for motor vehicles. The convenience control system comprises, in addition to a central locking control system for a plurality of doors and a tailgate of a motor vehicle, a control system for a window lifting mechanism, outside mirrors, a lock/unlock switch on a driver's door, an interior illumination system as well as an overall diagnostic system. Each of the system components has an actuator of its own, whose controller is controlled either by a decentralized control unit of its own or directly by a control apparatus communicating with the decentralized control units.
In case of the known central locking or convenience control systems, a rapid temperature increase up to overheating causing a failure of the individual actuators or control units or of the entire system may occur both in the actuators and in the control units due to a large number of actuations primarily by the user.